Over the past several years there have been a number of reports illustrating the use of an online analytical technique to monitor metals in industrial process gas (see for instance Monkhouse, P.: “On-line diagnostic methods for metal species in industrial process gas”, Prog. Energy Combust Sci. 28 (2002) pp. 331–381). One method that has been demonstrated to be particularly promising is photo-fragmentation fluorescence (“PFF”) of which Excimer Laser Induced Fragmentation Fluorescence (“ELIF”) is a variant that utilizes the high-energy ultraviolet light from an excimer laser as the excitation source. To date, a number of authors have explored the use of ELIF in industrial applications specifically to determine alkali concentrations in solid fuel combustors (K. J. Rensberger Welland, et al., Appl. Opt. 32 (1993) pp. 4066–4073; K. T. Hartinger, et al., Proc. Comb. Inst. 25 (1994) pp. 193–199; B. L. Chadwick, et al., Anal. Chem. 67 (1995) pp. 710–716; F. Greger, et al., Proc. Comb. Inst. 26 (1996) pp. 3301–3307; P. G. Griffin, et al., Rev. Sci. Instrum. 69 (1998) pp. 3874–3677; and U. Gottwald, et al., Appl. Phys. B 69 (1999) pp. 151–154). This prior work has shown that this method is capable of detecting sodium hydroxide and sodium chloride concentrations in the part per billion range (“ppb”) at temperatures as high as 1000° C.
The general technical approach of the method is to illuminate the atmosphere that contains simple molecular metal-containing species, such as NaOH, NaCl, KOH, etc., with a pulse of laser light (in this case with a 193-nm beam from an argon fluoride (ArF) excimer laser). The subsequent photo-dissociation results in a population of excited metal atoms that produce one or more atomic fluorescence lines that are easily detected.
There are a number of potential applications of this nearly real-time analytical technique in addition to solid fuel combustion diagnostics. In our case, understanding the behavior of alkali metals in glass furnaces is an especially attractive application because of two important practical issues surrounding the role of sodium in the atmosphere of a glass-making furnace. Sodium volatilization from the melt to the vapor phase in the furnace and into the exhaust can directly effect the formation of particulates and indirectly affect the durability of the furnace over time. This may be especially true for furnaces operating with pure oxygen in place of air in the burners.
Given the important role alkali vapor plays in practical operation of furnaces, it is desirable to make direct measurements of alkali metal concentration within the furnace atmosphere. All recent thermodynamic studies of the relevant chemistry of volatilized alkali metals indicate that greater than 99% of the sodium or potassium in the furnace atmosphere exist in the form of a metal hydroxide vapor, i.e., as either NaOH or KOH. All currently practical, analytical methods for measuring sodium and potassium in glass furnaces are performed using extractive sampling followed by analysis of the hot vapor, of a liquid condensate, or of both. In contrast, the present application is drawn to a method and an apparatus for providing real time data that can be used to optimize furnace operation.